A conventional solution for coding, e.g. audio, is to quantize low-frequency regions of the input signal in an encoder, and reconstruct high-frequency regions of the spectra at the decoder according to a reconstruction codebook. In this way all bits are allocated to the frequency components below a pre-defined frequency threshold or index, and at the decoder the remaining (unquantized) frequency components are reconstructed from the quantized frequency components.
A more advanced solution, which is suitable for variable bit rates, is to dynamically detect the regions to be quantized and regions to be reconstructed based on, e.g., the energy in frequency bands of the input.
Furthermore, it has been proposed to adjust the size of regions to be quantized based on the degree of difficulty for encoding the regions of the input signal in question. The region is smaller when it contains a spectrum that is difficult to quantize, and vice versa.
In spite of the above mentioned, there is still a need for an improved scheme for audio coding.